Function: Validate blog URL and title provided at signup.

Function: Add the appropriate errors to a WP_Error object, given results of a validation test.

Function: Validate a user name and email address when creating a new user.

Function: Check that an email address is valid for use.

Function: Add BuddyPress-specific items to the illegal_names array.

Function: Flush illegal names by getting and setting ‘illegal_names’ site option.

Function: Delete last_activity data for the user when the user is deleted.